Process for the preparation of distarch phosphate and the resulting product



United States Patent PROCESS FOR THE PREPARATION OF DISTARCH PHOSPHATE AND THE RESULTING PRODUCT Ralph W. Kerr, Riverside, and Frank C. Cleveland, Jr., Chicago, Ill., assignors to Corn Products Refining Cone pany, New York, N. Y., a corporafion of New Jersey No Drawing. Application August 6, 1954, Serial No. 448,359

16 Claims. (Cl. 260-2335) This invention relates to the preparation of starch phosphate esters wherein the colloidal properties of the starch have,been altered primarily by the introduction of distarch phosphate groups, i; e., phosphate cross-linkages, as contrasted to simple monostarch phosphate ester groups. More particularly the invention relates to a process of preparing distarch phosphate esters which retain the granule form of the starch.

Starch phosphate esters which are cross-linked have unusual properties which make them suitable for a number of industrial uses. They are more resistant to gelatinization and pastes made therefrom have increased stability as concerns breakdown by heating compared to untreated starch. In fact, depending upon the degree of crosslinking, starch esters may 'be prepared which are nongelatinizable in boiling water. a

In our c'opending application, Serial No. 388,914, filed October 28, 1953, now abandoned, there are described and claimed methods for making phosphate esters by heating starch in semi-dry form with salts of anhydro forms of phosphoric acid, such as, metaphosphate, polymetaphosphates, pyrophosphates and polyphosphates. After cooling, the starch phosphate is washed to remove impurities. Depending upon conditions, several type of products result: (1) monostarch phosphate, (2) distarch phosphates, and (3) monostarch phosphates wherein there is also an appreciable percentage of distarch phosphate groups.

The methods referred to above possess the inherent disadvantage that in order to remove unreacted salts and by-products an extensive washing step after the dry reaction and an additional drying step are necessary. Rewashing and redrying are not only cumbersome operations in starch manufacturing plants but are also relatively costly.

It is an object of this invention to provide a new and novel process for the production of distarch phosphate esters in granule form. Other objects will appear here inafter.

We have discovered that distarch phosphate in granule form may be produced by heating an aqueous slurry of ungelatinized starch with a water soluble metaphosphate salt at a temperature sufficiently low to maintain the starch in the unswollen granule state, the pH of the system being preferably at least about 9.0.

The reaction between starch and a metaphosphate salt is understood to proceed as follows:

(Sodium trimetaphosphate) Patented July 30, 1957 (T 0 0 Na Na R (Acid sulium py ophosphate) (Distarch phosphate) Under certain conditions some monostarch phosphate groups may also be produced but, if so, the amount will be negligible.

The obvious changes accompanying a starch crosslinking reaction are as follows: In the early stages of the reaction, the paste viscosity of the starch increases significantly. In contrast to simple esterificatiou, however, which also may produce increased paste viscosity, clarity of the cross-linked starch paste does not increase in proportion. Also in contrast to simple esterification, the pastes of cross-linked cereal starches become shorter and more salve-like (or less cohesive). The opposite is true in simple esterification, after which the pastes have higher clarity and longer flow.

As the crosslinking reaction progresses, viscosity reaches a peak and then declines to very low values; simultaneously shortness and opacity increase. (Clarity decreases.) This is due to a progressive decrease in the ability of starch substance to disperse in water as it becomes progressively more cross-linked. However, in these more advanced stages of cross-linking of starch in granule form, the starch may develop relatively high and stable viscosities if gelatinization conditions are made more strenuous such, as for example, greatly prolonging the cooking time, using autoclave temperatures or adding starch dispersing agents, such as alkali, acid or sugars. Technically, these are important characteristics in that more rugged starches are produced which are stabilized to break down by conditions employed by those who use the starch. For example, the relatively tender Waxy starches, such as waxy maize, or the non-cereal starches, such as tapioca, which rapidly deteriorate on cooking in many uses to a thin, slimy paste, may be stabilized by the correct amount of cross-linking so that they actually increase in viscosity as cooking time is extended. Moreover, the cohesiveness of these gels is reduced to a more palatable texture. The same may be said for certain derivatives of the cereal starches, such as corn monostarch phosphates (like the potato and tapioca starches they so strongly resemble). They also tend to deteriorate on prolonged cooking or at autoclave temperatures or under other adverse conditions more readily than untreated cereal starch. A definite amount of cross-linking converts corn monostarch phosphate into a product quite similar to a cross-linked waxy starch. This is an important development in that some of the undesirable characteristics of starches, such as corn starch, can be changed to desirable characteristics. Fi nally, in the last stages of cross-linking, the starch becomes insolubilized. Starch in the granule state containing a sufiicient number of distarch phosphate groups will not gelatinize even when boiled in water. Such a product may be used as an inert dusting powder, unaffected by'moisture or temperature, such as is used in steam sterilization. The product may, accordingly, he used for dusting and lubrication of surgeons gloves which may be sterilized in the autoclave and the starch will not lose its lubricating or de-tackifying effect.

The process of the present invention is simple and accordingly can be carried out with no difiiculty. A slurry of ungelatinized starch in Water containing the requisite amount of metaphosphate and having a suitable pH is See: Kerr: Chemistry and Industry of Starch, 2nd ed., page 470.

tion in the former case.

heated .with agitation at a temperature sufliciently low to maintain the starch in the unswollen granule state. In general temperatures between 40 C. and 50 C. are satisfactory, but higher or lower temperatures may be used depending on alkalinity and whether a gelatinization inhibitor is used. After the reaction has proceeded to the desired degree, the resultant distarch phosphate is filtered, washed, the pH adjusted andthe pro-duct dried.

The invention is applicable to all varieties of raw starch, e. g., corn, tapioca, wheat, waxy sorghum, grain sorghum and the like. Further, the invention is applicable to various modified starches and derivatives of starch, e. g., thin boiling starches, oxidized starches, starch ethers, starch esters and the like. The term starch, as used in the claims, is intended to include all of the above listed substances. As previously mentioned, the phosphorylating agents are 'the water soluble metaphosphates and polymetaphosphates andof these sodium trimetaphosphate is the preferred reagent. Although some commercial samples of oth r p espha es ea, dium t i yph p p duced an appreciable degree of esterification of starch in aqueous slurry, others did not, and it is thought that metaphosphate impurities were responsible for the esterifica- The pyrophosphates appear to give very little, if any, reaction with starch in the wet state.

The phosphorylation of starch in accordance with the present invention proceeds more efficiently at a high pH,

preferably at 11.0 or above although a pH of about 9.0

is satisfactory. Various alkaline materials, e. g., sodium hydroxide, sodium carbonate, lime, and the like may be used to make the pH adjustment.

The amount of metaphosphate required to produce cross-linking sufficient to show an increase in the viscosity of starch is quite small, i. e., of the order of about 0.03 percent, based on the dry weight of the starch, when the time of the reaction is one hour, the temperature of 50 C., and the pH 11. Under these same conditions of time, temperature and pH, about 0.6 percent of metaphosphate will make the starch nongelatinizable in boiling water. Although amounts higher than about 0.6 percent are not detrimental for these conditions, such amounts serve no useful purpose. The reaction proceeds faster with increased temperature, and pH, and with increased amount of metaphosphate up to the point where the starch becomes nongelatinizable. If temperatures below 50 C. are used, it is obvious that correspondingly more metaphosphate should be used if time and pH are the same. A practical operating range of metaphosphate is about 0.01 to about 3 percent.

It has been found that the concentration of sodium added as a sodium salt has an effect on the degree of .phosphorylation, the higher the concentration (within practical limits) the higher the degree of phosphorylation. A total sodium ion concentration of about 0.4 mole per liter gives satisfactory results.

The following examples, which are intended as typical and informative and in no way limiting the invention, will further illustrate the invention.

EXAMPLE 1 Production of high viscosity, partially cross-linked corn starch: the effect of time on the reaction between starch and sodium trimetaphosphate in aqueous slurry at pH 10.2 and 50 One mole of corn starch (180 grams at percent moisture content) was suspended in 3 25 ml. of water into which had been dissolved 3.3 grams of commercial sodium trimetaphosphate (Victor Chemical Company) and suflicient sodium carbonate buffer (5.45 grams) to adjust the pH of the starch slurry to 10.2. The slurry was heated to 50 C. with stirring and held at this reaction temperature. Samples were removed at intervals shown in Table I, filtered, washed and adjusted to pH 6.7

with hydrochloric acid and dried.

Scott viscosity tests were made on these samples in accordance with procedures described in Kerr, Chemistry and Industry of Starch, 2nd edition, pp. 119-121. Results were as follows:

.Table I REACTION OF CORN STARCH WITH SODIUM TRIMETA- PHOSPHATE 2% IN AQUEOUS ,sLuRaY AT pH 10.2 AND C.

Reaction time, Scott viscosity 1 Min.: sec/50 ml. 0 (untreated) 93 40 105 50 147 Unless otherwise specified, viscosity tests were run using 15 grams of starch at 12 percent moisture content in 280 ml. wa er- The viscosity-of the heatgelatinized samples increased to a maximum in about 50 minutes reaction time and then decreased as the cross-linking reaction continued. -A sample taken from the reaction mixture after 24 hours would not gelatim'ze when boiled in .water.

The high viscosity .sampletaken after 50 minutes reaction time formed a paste which was more opaque and less cohesive than untreated corn starch and by analysis had a phosphorus content of 0.03 percent. This starch when made into adhesive formulations suitable for pasting paper products, such as paper bags or corrugated paper board, gave higher bodied pastes which permitted the use of greater dilutions than untreated corn starch; moreover, the cross-linked starch paste had better stability with use, that is, maintained its viscosity with time and a it on better than un r a ed n rc EXAMPLE 2 Procedures given in Example 1 were repeated with the exception that only one gram of sodium trimetaphosphate was used per 180 grams of corn starch (at 10 percent moisture content) and 6.65 grams of sodium carbonate was added.

Samples were removed at time intervals shown in Table II, washed, neutralized and dried. Paste clarity of pastes made from these samples was determined as follows: A slurry of the starch product in water is adjusted to pH 6.5 and at about 1 percent concentration. The flask is then immersed in boiling water for 30 minutes with occasional stirring, hen cooled to 25 C. and adjusted in volume so as to contain 1 gram starch per ml. At 25 C,, the paste is introduced into a 13 mm. cell of a Coleman spectrophotometer, the light wave adjusted to .=650 m and the percent light transmission-determined, using distilled water as reference for 100 percent light transmission.

, Table II REACTION OF SODIUM T-RIMETAPHQSPHATE WITH CORN STARCH (ONE GRAM/ si) GRAMS) IN AQUEOUS SLURRY AT'pH 10.2 AND 50 0.

Clarity of 1% Scott Vis- Pastas As Per- Reaction Time, Min. cosity, Sec./ cent Light 60 ml. Transmission at )\=650 m trimetaphosphate under theseconditions was to retard the esterification so that now the peak viscosity starch phosphate was not obtained until approximately 80 minutes reaction time.

EXAMPLE 3 The effect of lower trimetaphosphate concentration in aqueous starch slurries at the higher pH value of 11 and at 50 C. Even still lower trimetaphosphate concentrations than used in Examples 1 and 2 were found to be effective in producing all degrees of cross-linking in corn starch. However, the reaction was accelerated by using the higher pH value of 11 in this experiment.

One molar weight of corn starch was stirred into 220 ml. of water into which had been dissolved 4.52 grams of sodium carbonate and the amounts of sodium trimetaphosphate shown in Table ,III. Just prior to adding the starch, 4 ml. of 10 N sodium hydroxide was stirred into the reaction solution. The pH value of the slurry was 11. The reaction mixture was held at 50 C. for one hour then cooled to room temperature, adjusted to pH 6.5 with hydrochloric acid, washed and dried. A series of such reactions was run using varying amounts of sodium trimetaphosphate between 0.05 and 1.0 gram. The Scott viscosities of these products are shown in Table III.

Table III EFFECT OF LOWER TRIMETAPHOSPHATE CONCENTRA- TIONS ON AQUEOUS SLURRIES F STARCH AT pH 11 (50 C. FOR ONE HOUR) Sodium Trlmetaphosphate Added For Scott Vis- Stormer 180 g. Corn Starch, grams coslty, es

Sec/60 ml. Sec/50 rev.

0 (untreated) 94 Gel. 0.05 120 Too thick It will be observed from the results in Table III that at pH 11 and 50 C. as little as 0.15 gram of sodium trimetaphosphate per 180 grams corn starch at percent moisture content produced a peak Scott viscosity starch product within one hour by the aqueous slurry method.

Under these conditions also, as little as 0.75 to 1.0 gram of sodium trimetaphosphate produced a starch product so completely cross-linked that when it was held in boiling water bath for 15 minutes, it had no Scott viscosity that could not be accounted for by 15 grams of unswollen starch granules in 280 ml. of water. Water alone gives a Scott viscosity of 11 seconds.

This example illustrates additionally the higher reaction rate at pH 11 then was obtained at pH 10.2 in Examples 1 and 2.

Pastes of several of the products used for Scott viscosity were cooled to 25 C. and after one hour at this temperature were placed in the cup of a Storrner viscometer. A 175 gram weight was used to actuate the spindle and the seconds noted for 50 revolutions. As indicated in Table III pastes made from untreated corn starch set to a rigid gel after one hour and pastes from starch treated with 0.05 and 0.10 gram of trimetaphosphate, were too thick to measure by this test. The peak Scott test starch however was fluid, although quite thick and relatively short in body. As the concentration'of trimetaphosphate used was increased, cold paste body at one hour decreased until finally only a watery suspension was obtained. As the extent of cross-linking was increased the cold pastes-became increasingly less cohesive and salve-like. a

6 EXAMPLE 4 Efiect of added cation on the reaction between trimetaphosphate and starch in aqueous slurry.

The equation given for this reaction between starch and trimetaphosphate indicates that acid groups (acid sodium pyrophosphate) are produced during the reaction. Since the reaction proceeds more readily at higher pH values one function of the added carbonate in Examples 1 to 3 is to act as buffer. However, the added sodium also appears to act beneficially on the phosphorylation as well. If sufiicient alkali is added to maintain a high pH value then on a molar basis, sodium in NaCl is as effective as in NazCOa.

Three reaction mixtures were set up as follows: 180 grams of corn starch (at 10 percent moisture content) was stirred in 320 ml. of water into which had been dissolved one gram of sodium trimetaphosphate and 4 ml. of 10 N NaOH. To one, 4.52 grams of NazCOa was also included and to a second, 5 grams of NaCl had been added; the third contained no further additions. All three were stirred for 2 hours at 50 C., then cooled, neutralized with HCl, washed with water and dried.

Data on these products are shown in Table IV.

Table IV EFFECT OF SODIUM CONCENTRATION ON THE REAC TION BETWEEN STARCH AND TRIMETAPHOSPHATE Additions of Sodium in Total MolesX10- ml. from- Sodium Ooncen- Scott Stormertration Vis., Test,

in See/50 See/50 (Na-P om NaOH NaCl N 32003 Mnlesx ml. rev.

10 Per 100 ml.

EXAMPLE 5 Use of lime as catalyst instead of sodium hydroxide and carbonate to produce a peak Scott viscosity corn starch diphosphate.

One molar weight of corn starch was stirred into 255 ml. of water into which had been dissolved 2.37 grams of commercial calcium hydroxide (assay 93 percent) and 0.81 gram of sodium trimetaphosphate. The slurry was stirred for 2 hours at 45 C. and then cooled to room temperature. The pH was 11.5.

The slurry was filtered, washed with water and adjusted to pH 6.2 with hydrochloric acid.

A high viscosity, partially cross-linked starch resulted having a Scott viscosity test of second per 50 ml.

EXAMPLE 6 1100 grams of corn starch was stirred into 1300 ml. of

: water into which had been dissolved 33 grams of sodium At the end of this time, the slurry was cooled to room tempera ure and-a ortion (part .A) was removed, -adjusted to pH 6,; with hydrochloric acid, thoroughly washed .in water and. dried.

During purification-of the balance (part B .of the reaction mixture sufficient ;calcium chloride was added so .that 'when washing ,of the product was .terminated and the product dried, thestarch powder contained an amount of calcium equivalent .to 0.25 percentcalcium phosphate.

This dry starch powder was ,found to be very mobile and usable "as a dusting powder, particularly as a surgical rubber dusting vpowder, becauseof its great. resistance to gelatinization, as shown below; surgical rubber gloves are sterilized before use bysteam autoclaving and accordingly any dusting powder used on the gloves must withstand steam sterilization.

Both starch products madeinvthis example were treated ,as follows: 5 grams of product was stirred into 100 m1. of water and heated in a boiling water bath for minutes. Ihe heatedrmixture was adjusted to 100 ml. in volume and poured into :a 100 ml. graduated cylinder. After 24 hoursatgroom temperature it was-noted that substantially allof the starch had settled out. The .volume of sedimented starch was noted and is shown below. Two other commercial starch products sold under the trademarks Biosorb and Vulca-IOO, as non-gelatinizing products were tested in comparison.

EXAMPLE -7 Effect off pHvalue on thereaction of starch in aqueous slurry with sodium trimetaphosphate.

Procedures, substantially the same as giveninExample 2 were repeated with the exception that either sufiicient sodium hydroxide or hydrochloric acid was incorporated into the formulation to, give reaction pH values of approximately ll, 9 and 8, instead of 'the pH value of approximately 10, used in Example 2. Below in'Table VI are the results of these experiments compared to those of Example 2 using Scott test as a measure of reaction.

Table VI BEA'CTION 'OF AQUEOUS 'SIJURRIES OF CORN STAROH WITH SODIUMTRIMETAPHOSPHATE AT 0. AND AT pH VALUES OF 3, 9, 10 AND 11 Scott Viscosity Values OtProducts from Reactions at pH. Values Reaction Time, Min.

pH8 pH9 pHlO pH11 g (untreated) The results show the great retardation in rate of crosslinking by-trimetaphosphate when the pH-value is lowered over the range from ,11 to 18. Whereas .atpH l Lathe peak viscosity occurred within the first 5 minutes, at -.pH 10 the time was about minutes, ffQl pH 9 sometime after 180 minutes and at pH 8 sometime after 24 hours. Extensive crosselinking .(Scott values less than 20) requires 'less than'2 hours at pH 11, 5 hours at pH 10; about 48 ho rs atpI-I 9 .and may not occurat all at pH 8, since the ,reagent is hydrolyzed within several days at this temperature ndpH EXAMPLE v8 Production of partially cross-linked .waxy ,sorghum starch with trimetaphosphate !in aqueous :slurry at pH 10.2; stabilized waxy starch.

350 grams of waxy ;grain :sorghum starch was stirred into 648' ml. of water into which ;had been dissolved 2 grams of sodium trimetaphosphate and 13.3 grams of sodium carbonate. TIfhe pHof this slurry was 10.2. The slurry was .stirred at 50 C. and samples were removed at time intervals .shown in Table :VII. These samples Were filtered, -the starch product washed in water, adjusted to pH 6.0 with hydrochloric acid, filtered anddried. -V iscosity. characteristicsof these cross-linked-waxystarches are shown below.

Table "VII REACTION -OF AQUEOUS SLURRIES OF WAXY GRAIN SORgggM S'gAROH WITH TRIMETAPHOSPHATE AT pH 10.2 50

Clarity of 1% Pastas as Percent Scott Vis- Stormer Reaction Time, Min. Light .cosity," est,

Transmis- Sec/50 ml. Sec./50 rev.

a In thesetcsts only 12 grams of starch product was used in 280 ml. of water.

Again a cross-linking reaction is indicated by the results that as the reaction progressed the Scott viscosity increased to a maximum and then rapidly decreased. Progressively with "this change, the cohesive nature of cooked and cooled waxy starch became less.

The productmade at 75 minutes reaction time, that is, with a degree of cross-linking considerably more than enough to bringthe starchproduct to a peak viscosity, is a type ofstabilized-waxy starch product of considerable technical importance. When untreated waxy sorghum or waxy maize starch is gelatinized in water at the boiling point the viscosity increases rapidly to a very 'high'value and then progressively decreases to very low values. Cold pastes are long and slimyand as cooking progresse s, they become relatively thin inconsistency. The deterioration of waxy .starch on cooking is accentuated by the'presence ofacids and sugars. Therefore, although waxy starches have inherently ,the properties of giving pastes of :high .clarity and freedom from set back to irreversible .ge'ls vthey :are not acceptable as thickening agents in many-applications,ssuchzas, -for example, making of fruit.pies, production of gum confections, such as .gum. drops.or..orange slices, and the canning of cream style corn. :However, the waxy starch with a degree of -cross linking as represented by the sample produced in 75 :minutes reaction ;time, is eminently suited foruse.-as a thickening agent for applications aboverenumeratedas well as many others because of the stabilization'ofviscosity efiected by the phosphate cross-linking. As the starch product is cooked, the viscosity rapidly approaches a useable value and thereafter the viscosity remains relatively constant. Even when cooked in the presence of acids, such as citric, or sugars, or cooked under pressure, the pastes show a remarkable stability. As these pastes are cooled, they remain fluid and of acceptable body and moreover, the texture is very much less cohesive and slimy than untreated waxy starch pastes.

EXAMPLE 9 Stabilizing corn monostarch phosphate by treatment in aqueous slurry with trimetaphosphate.

Corn starch was esterified in a semidry reaction with sodium tn'polyphosphate, in accordance with the method described in copending application, Serial No. 388,914, filed October 28, 1953, as follows: One molar weight of corn starch (180 grams at IO percent moisture) was stirred into 215 ml. of water into which had been dissolved 15.5 grams of sodium tripolyphosphate. The pH was approximately 8.5. The starch was filtered by suction to form a cake of approximately 45 percent moisture content. This was dried at 60 C. to approximately 12 percent moisture content. By analysis, 9 grams of the polyphosphate (0.08 mol calculated as a sodium monophosphate) was retained by the starch, the balance being in the aqueous filtrate.

This starch was now heated with stirring, and with provision for moisture removal, at temperatures between 120 and 130 C. and then cooled. The starch product suspended in 250 ml. of water, now showed a pH of 7.0. It was filtered and washed twice more by suspension in 250 m1. of water followed by filtration with suction. The starch was then dried to a commercial moisture content of approximately percent for a powdered starch.

The product contained 0.37 percent phosphorus, equivalent to a starch phosphate ester with a D. S. of 0.03 as orthophosphate groups. The starch when gelatinized by heating in water formed a very viscous sol (as indicated by Scott viscosity value) with little or no tendency to gel or increase in viscosity with age (as indicated by Stormer consistency values). The sol had very high clarity compared to untreated corn starch (both measured at pH 6.5) and had long flow characteristics similar to tuber or waxy starches. I

The monostarch phosphate thus obtained was treated in an aqueous slurry with sodium trimetaphosphate by procedures the same as used in Example 8. A product was obtained with stabilized paste properties quite similar to the 75 minute reaction product of the waxy sorghum starch of Example 8; the untreated monostarch phosphate showed unstable paste properties similar to untreated waxy sorghum starch.

EXAMPLE 10 Stabilizing hydroxyethyl starch ether by treatment in aqueous slurry with trimetaphosphate.

A commercial sample of hydroxyethyl starch, of low D. S. (0.05) and in the granule state was stabilized by introducing phosphate cross-linkages as follows: 162 grams (dry basis) of the starch ether was stirred into 324 ml. of water into which had been dissolved one gram of sodium trimetaphosphate and 6.66 grams of sodium carbonate. The pH value of the slurry was 10.2. The slurry was heated at 50 C. and samples were removed at time intervals, as shown below. These samples were cooled to room temperature, adjusted to pH 6.5 with hydrochloric acid, filtered, washed in water and dried.

Scott viscosities and Stormer consistency values were determined using 13 grams of product (at 12 percent moisture content) in 280 ml. of water.

Table VIII Stormer Consistency, Scott Vis- Sec. [50 revolutions Reaction Time, Min. cosity,

See/50 ml.

1. hr. at 24 hrs. at

0 (untreated, HE-starch) 89 171 205 30 47 76 86 28 51 56 120 25 40 41 Peak viscosity was reached between 0 and 30 minutes but was not measured.

It will be observed that as cross-linking progressed, the product showed progressively less tendency to thicken up when pasted, cooled and aged. Moreover, the ether which had been cross-linked by trimetaphosphate treatment (for example, the product at 120 minutes) was more stable at elevated temperatures and formed a less slimy paste when cold. The latter change in character is desirable in many applications for applying adhesives and sizes made from modified starches.

EXAMPLE 1 l Stabilizing an oxidized thin boiling corn starch by treatment in aqueous slurry with sodium trimetaphosphate.

A commercial sample of a thin boiling starch, made by oxidizing corn starch in the granule state with alkaline sodium hypochlorite was treated as follows: 180 grams of the starch at 10 percent moisture content was stirred into 220 ml. of water into which had been dissolved 3.3 grams of sodium trimetaphosphate, 4.52 grams of sodium carbonate and sufficient sodium hydroxide to adjust the final slurry to pH 11. The starch slurry was stirred and heated at 50 C. for 90 minutes. The slurry was cooled and filtered and the starch, still in the granule state, was washed in water, neutralized with hydrochloric acid, filtered and dried.

Scott viscosity was determined using 28.35 grams of starch in 280 ml. of water and found to be 102 seconds per ml. A duplicate viscosity determination was run with the exception that the paste was held in a boiling water bath for 90 minutes instead of the 15 minutes, used in the Scott test. The viscosity was now 72 seconds per 100 ml. An otherwise untreated, oxidized corn starch commonly used in textile sizing operations was tested similarly. The Scott test (28.25 g. in 280 ml.) was 108 after the usual 15 minute pasting period. Heated for 90 minutes in a boiling water bath, however, the viscosity was now only 32 seconds. Thus the untreated oxidized starch had lost about 70 percent of its viscosity on being held for 75 minutes in the vicinity of holding temperatures used in textile mills for sizes, such as, for example, warp sizes. This loss amounts to almost 1 percent per minute and is highly objectionable from a textile sizing operation standpoint. The stabilized, oxidized starch of this example, however, lost only 29.4 percent of its viscosity during a comparable period. Moreover, the paste of the stabilized starch set back, or jelled, less on cooling and standing, and added advantage in mills where left over size is held from one days operation to the next.

EXAMPLE 12 Cross-linking corn starch with sodium metaphosphate.

A sample of commercial sodium metaphosphate was found to be partially insoluble in water. About 60 percent of the sample dissolved. The dissolved portion which contained one gram of dry solids was included in the 324 ml. of make-up water in which grams of corn starch was suspended. 6.66 grams of NazCOs was added and the final pH value of the starch slurry was 10.2. The slurry was stirred at 50 C. and periodically samples were removed, adjusted to pH 6.5 with HCl, filtered,

f1 washed in water and dried. Scott viscosities of these products are shown in Table IX.

Table IX REAGTION F SODIUM METAPHOSPBATE' \VITH CORN STARCH (ONE GRAM/180 G RAMS) IN AQUEOUS SLURRY AT pH 10.2 AND C.

Clarity of 1% Scott Pastas as Reaction Time, Min. Viscosity, Percent Light Sea/50 ml. Transmission at A=650 mg 0 (untreated) 93 20 45.-. 110 139 21 146 159 19 123 120. 104 l I80- 55 I 1* 240. 29 l 360'. 17 12. 5

Comparing these results with those given in Table ll, Example 2, where one gram of sodium trimetaphosphate was used per grams of corn starch in aqueous slurry at pH 10.2 and 50 C., it is apparent that the action of sodium metaphosphate is comparable to that of sodium trimetaphosphate.

EXAMPLE l3 Cross-linking corn starch with sodium hexametaphosphate Corn starch was made into a slurry with a 10 percent aqueous solution of sodium hexametaphosphate that contained sufficient sodium hydroxide to give a pH value of 11.1. to the final. reaction mixture. The aqueous suspension. had a density corresponding to 22 B. at 30 C. The reaction mixture was stirred at 50 C. for 24 hours then cooled, adjusted from pH 11.0 to 6.5 with hydrochloric acid, filtered, thoroughly washed and dried.

The dried product when resuspended in water and heated for 15 minutes in a boiling water bath as in running the Scott viscosity by determination remained substantially ungelatini'zed.

EXAMPLE 14 Use of distarch phosphate inv cherry pie fillings Canned cherry pie fillings were prepared as follows: 3.5 lbs. of distarch phosphate, as prepared in accordance with Example 8, was stirred into 16 lbs. of water to make a slurry.

This slurry was added to a batch of cooked cherries prepared as indicated below:

A mix was made up of the following ingredients:

Drained cherries (frozen and thawed) (5 parts The mix was stirred slowly while cooking to F. At this time the distarch phosphate slurry was added and the temperature was raised to and held at 196 F. for 10 minutes.

Thereupon the hot prepared pie fillings were poured into cans and sealed. The cans were then immersed in boiling water for 10 minutes and cooled to room temperature.

Cherry pie fillings were similarly prepared using untreated waxy sorghum starch.

At periodic intervals, over several weeks time, cans of each of the two pie fillings were opened. Fillings made containing the distarch phosphate remained fluid but of satisfactory consistency and the liquidportion wasclean- Fillings made of untreated Waxy starch were un- 12 acceptably fiuid as made, and after about two days, were oia watery consistency.

Cherry pies were made and baked from both types of fillings. The cherry pie fillings made from the distarch phosphate were fluid, of a very desirable consistency, clear and of a very attractive appearance. Those made frorn 'untreated: waxy sorghum starch were unacceptably thinhodied-so that much of the juice ran out of the pie. In comparison, fillings similarly made and used, employing untreated corn starch were opaque, whitish in appearance and gel-like in consistency.

EXAMPLE 15 Use of distarch phosphate in cream style COrn In canning sweetcorn (cream style), field tests have shown that distarch phosphate: prepared in accordance with Example 9 gave. the same consistency to cream. style corn as twice the weightof untreated corn starch. Moreover, the consistency was smoother with distarch phosphate since it was superior in preventing curdling. of. the sweet corn protein during the cooking and canning operation.

We claim:

1. A process for making distarch phosphate which comprises treating unswollen granule starch in aqueous slurry with a water soluble salt from the group consisting of metaphosphates andpolymetaphosphates at a temperature sufficiently low to maintain: the starch in the unswollen granule state for a time to effect the desireddcgree of esterification, the amount of said salt being. at least about 0.01 percent, based on the dry Weight of the starch.

2. Process according to claim 1 wherein the soluble salt is sodium trimetaphosphate.

3 Process according to claim 2 wherein the sodium ionv concentration is'maintained at at least about 0.4 mole per liter.

4. Process according to claim 1 wherein the soluble salt is sodium metaphosphate.

5. Process according to claim 4 wherein the sodium ion concentration is maintained at at least about 0.4 mole per liter.

6. Process according to claim 1 wherein the soluble salt is sodium hexametaph'osphate.

7. Process according to claim 6 wherein the sodium ion concentration is maintained at at least about 0.4 mole per liter.

8. A process for making distarch phosphate'which comprises treating unswollen granule starch in aqueous slurry with a water soluble salt from the group consisting of metaphosphates and polymetaphosphates in the amount of at least about 0.01 percent, based on the dry weight of the starch, at a temperature suffioiently low to maintain the starch in unswollen granule state, and for a time to efiect-the desired degree of esterification, the pH of the system being maintained at at least about 9.0,, thereafter neutralizing the system and washing and drying the resultant distarch phosphate.

9. Process according to claim 8 wherein the soluble salt is sodium metaphosphate.

10. Process according to claim 9 wherein the sodium ion concentration is maintained at at least about 0.4 mole per liter during esterification.

11. A process for making corn distarch phosphate which comprises treating unswollen granule corn monostarch phosphate in aqueous slurry with sodium trimetaphosphate under non-swelling conditions, the pH of the system being at least about 9.0, neutralizing the system and washing and drying the resultant distarch phosphate.

12. A process for making distarch phosphate which comprises treating unswollen granule monostarch phosphate in aqueous slurry with a. water soluble salt from the group consisting of metaphosphates and polymetaphosphates at a temperature sufiiciently low to maintain the'monostarch phosphate in the unswollen granule state 13 the pH of the system being maintained at at least about 9.0 and the amount of salt being at least about 0.01 percent, based on the dry weight of the monostarch phosphate.

13. A process for making partially cross-linked distarch phosphates which comprises treating unswollen granule starch in aqueous slurry with a water soluble salt from the group consisting of metaphosphates and polymetaphosphates in the amount of at least about 0.01 percent, based on the dryweight of the starch, at a temperature sufliciently low to maintain the starch in the unswollen granule state for a time sufl'icient to form a product which is insoluble in cold water but which gelatinizes in boiling water to give a paste, the viscosity of which is stable against breakdown due to agitation, pressure and heat.

14 Product according to claim 13.

15, A process for making corn distarch phosphates which comprises treating unswollen granule corn starch in aqueous slurry with a water soluble salt from the group consisting of metaphosphates and polymetaphosphates in the amount of at least about 0.01 percent, based on the dry weight of the starch, at a temperature sufficiently low to maintain the starch in unswollen granule state until the Scott viscosity of a paste increases from about 90 to about 190 seconds per 50 ml. using 15 grams of starch product in 280 ml. of water, the pH of the system being maintained at at least about 9.0, thereafter neutralizing the system and washing and drying the resultant distarch phosphate.

16. A process for making waxy grain distarch phosphate which comprises treating unswollen granule waxy grain starch in aqueous slurry with a water soluble salt from the group consisting of metaphosphates and polymetaphosphates in the amount of at least about 0.01 percent, based on the dry weight of the starch at a temperature sufliciently low to maintain the starch in unswollen granule state until the'Scott viscosity of a paste is reduced from about 160 to about to seconds per 50 m]. using 12 grams of starch product in 280 ml. of water, the pH of the system being maintained at at least about 9.0, thereafter neutralizing the system and washing and drying the resultant distarch phosphate.

References Cited in the file of this patent UNITED STATES PATENTS 2,252,479 Beyer Aug. 12, 1941 2,461,139 Caldwell Feb. 8, 1949 2,575,352 Lohmar Nov. 20, 1951 FOREIGN PATENTS 70,237 Switzerland May 8, 1913 

1. A PROCESS FOR MAKING DISTARCH PHOSPHATE WHICH COMPRISES TREATING UNSWOLLEN GRANULE STARCH IN AQUEOUS SLURRY WITH A WATER SOLUBLE SALT FROM THE GROUP CONSISTING OF METAPHOSPHATES AND POLYMETAPHOSPHATES AT A TEMPERATURE SUFFICIENTLY LOW TO MAINTAIN THE STARCH IN THE UNSWOLLEN GRANULE STATE FOR A TIME TO EFFECT THE DESIRED DEGREE 